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White paper on the relevance of the European Solar Telescope (EST) for the French heliophysics community
No full textThe project of the European Solar Telescope aims to provide a state-of-the art infrastructure to study the Sun and its interactions with Earth and the heliosphere. This 4.2m aperture telescope will be equipped with multi conjugate adaptive optics, light-polarisation analyser, imaging spectrograph and integral field unit spectrographs. It will provide unprecedented observations of the solar photosphere and chromosphere and of the dynamical events and features that pertains to the low solar atmosphere. The EST project is presently in a phase of crystallisation, aiming at the creation of an European Research Infrastructure Consortium. While the French community has continuously been associated with the development of the EST project, some specific scientific aspects are more particularly relevant for the French astrophysics and heliophysics communities. The present review highlights the scientific research axes of high interest from the French community that shall strongly benefit from EST. The later will not only advance numerous topics of solar physics, as well as solar adaptive optics developments, but will also provide unrivaled datasets of high interest in the framework of space weather. This review also aims to highlight the space weather use that can be done with future EST observations, that will be particularly relevant for French heliophysicists
Higher dualities in E exceptional field theory
No full textInternational audienceIt has been conjectured that there exists an E11-invariant formulation of eleven-dimensional supergravity in which the propagating fields of the theory are realised through an infinite tower of higher duals. In this work, we prove this conjecture explicitly within E11 exceptional field theory at the linearised level. Starting from the pseudo-Lagrangian, we construct parent actions for all higher gradient dual fields that are associated with the three-form, the six-form, and the dual graviton. We show that the resulting Euler-Lagrange equations constrain the Stueckelberg fields to be pure curls, ensuring that the higher duals propagate the same physical degrees of freedom as the original supergravity fields. The additional Stueckelberg fields, which are not predicted by the tensor hierarchy algebra, are shown to play a specific role as sources for the Labastida tensors of the higher dual fields
Galois groups of low dimensional abelian varieties over finite fields
No full textInternational audienceWe consider three isogeny invariants of abelian varieties over finite fields: the Galois group, Newton polygon, and the angle rank. Motivated by work of Dupuy, Kedlaya, and Zureick-Brown, we define a new invariant called the weighted permutation representation which encompasses all three of these invariants and use it to study the subtle relationships between them. We use this permutation representation to classify the triples of invariants that occur for abelian surfaces and simple abelian threefolds
Comparison of M10 and M20 Meteomodem radiosondes relative humidity measurements with ECMWF ERA5 above France: focus on the upper troposphere
No full textInternational audienceAccurate knowledge of the relative humidity (RH) in the troposphere is important for predicting cloud formation, particularly in the upper troposphere where contrails can form and contribute to global warming. However, it is difficult to predict their formation due to the lack of precise RH measurements at these altitudes. This paper compares RH data from Meteomodem radiosondes (M10 and M20) acquired over a 5-years period (2020-2024) at the Trappes and Nîmes meteorological stations in France with ECMWF ERA5 analyses, with a focus on the upper troposphere. For Trappes, two datasets exist: one processed operationally by Météo France (MF) and a second processed using the GRUAN standard. Whatever the processing is, Meteomodem radiosondes RH values are on average higher than ERA5 ones, by about 2 % at 800 hPa up to 10 % at 200 hPa. The operational MF processing generally gives higher RH than the GRUAN processing. The median difference between both processing methods is lower than 2.2 % for pressures higher than 300 hPa and is maximum for lower pressures and nighttime measurements, the GRUAN processing showing more consistency between daytime and nighttime measurements. The evolution of MF processing over time
H.E.S.S. detection of the PSR J0855-4644 nebula
No full textInternational audienceHESS J0852-463 is a TeV γ-ray source located in the Galactic plane. The region consists of a supernova remnant (SNR, RX J0852.0-4622) with a shell-like morphology, commonly referred to as Vela Junior, and a pulsar denoted PSR J0855-4644. Pulsars are among the most efficient leptonic accelerators in our Galaxy, making this region particularly interesting to study. We utilise the most recent data taken by the High Energy Stereoscopic System (H.E.S.S.), to investigate any γ-ray emission associated with the pulsar in this region, PSR J0855-4644. We applied a full forward folding method on the H.E.S.S. data. Utilising 3D modelling techniques, we evaluated the TeV γ-ray emission towards the various components of this complex system. The distinct energy-dependent morphology observed in our data motivates further investigation of this source. We resolved the emission in the Vela Junior region into various components, several of which correspond to the SNR itself. In particular, we find a new extended component which is coincident with the position of PSR J0855-4644. The spectrum follows a power-law distribution with a best-fit index of ΓE = 1.81 ± 0.07stat which differs from the properties of the surrounding γ-ray emission of the Vela Junior SNR. A one-zone leptonic joint fit between the X-rays (from XMM-Newton) and γ-rays (from H.E.S.S.) leads to a lower limit on the magnetic field of 1.6μG and a spectral index of α = 1.88 ± 0.01, in line with expectations of pulsar wind nebulae (PWNe). In this paper, we report the first detection of the PWN of PSR J0855-4644 at TeV energies with the H.E.S.S. experiment at a significance of 12.2σ. This is attributed to the advanced techniques of the 3D analysis. Based on the pulsar's characteristics, its PWN is consistent with the known TeV PWNe population in the Galaxy
Asymptotic behavior of some stochastic models in population dynamics: a Hamilton-Jacobi approach
No full textIn this paper, we investigate the asymptotic behavior of individual-based models describing the evolution of a population structured by a real trait, subject to selection and mutation. We consider two different sets of assumptions: first, the case of critical or subcritical branching population processes in a regime combining a discretization of the trait space, small mutations, large time and large initial population size, where we are able to characterize using a Hamilton-Jacobi approach, the survival set of the population, and the asymptotic of the logarithmic scaling of subpopulation sizes. Second, we generalize by a direct method the convergence to the classical Hamilton-Jacobi equation obtained in the super-critical branching regime considered in [6] to a more general trait space and under weaker assumptions. Moreover, we establish that the stochastic and the deterministic dynamics are asymptotically equivalent in large population
Persistent Nanophosphors: Poised to Outperform Bulk Counterparts?
No full textInternational audienceThe design of advanced materials often reveals how apparent imperfections, such as structural defects or impurities, can be transformed into functional advantages. In insulating oxide matrices, the controlled introduction of dopant ions is the first step toward efficient photoluminescence. Later, the engineering of additional defects, often detrimental for photoluminescence, gives rise to unique capabilities for optical energy storage and persistent luminescence. Initially driven by biomedical applications, nanomaterials currently occupy a central role in persistent phosphor research. However, elaboration processes allowing to preserve their nanoscale usually involve poor control over their crystallinity, leading to performance behind that of bulk materials. Developing nanophosphors with well‐defined morphology and energy levels engineered for tailor‐made and efficient energy storage presents a significant materials challenge. Yet once again, what seems a limitation may prove to be a powerful opportunity. By exploiting the nanoscale to engineer energy storage in an unprecedented manner, persistent nanophosphors can open a new era in advanced optical materials. This perspective highlights how emerging applications, progress in nanoscale synthesis, surface engineering, and integration into advanced architectures are opening the path toward multifunctional, application‐ready materials. Altogether, the nanoscale offers a transformative avenue that can enable persistent nanophosphors to outperform their bulk counterparts
Learning with Locally Private Examples by Inverse Weierstrass Private Stochastic Gradient Descent
No full textReleasing data once and for all under noninteractive Local Differential Privacy (LDP) enables complete data reusability, but the resulting noise may create bias in subsequent analyses. In this work, we leverage the Weierstrass transform to characterize this bias in binary classification. We prove that inverting this transform leads to a biascorrection method to compute unbiased estimates of nonlinear functions on examples released under LDP. We then build a novel stochastic gradient descent algorithm called Inverse Weierstrass Private SGD (IWP-SGD). It converges to the true population risk minimizer at a rate of O(1/n), with n the number of examples. We empirically validate IWP-SGD on binary classification tasks using synthetic and real-world datasets.30 pages, 8 figure
A short derivation of Boltzmann distribution and Gibbs entropy formula from the fundamental postulate
No full textIntroducing the Boltzmann distribution very early in a statistical thermodynamics course (in the spirit of Feynmann) has many didactic advantages, in particular that of easily deriving the Gibbs entropy formula. In this note, a short derivation is proposed from the fundamental postulate of statistical mechanics and basics calculations accessible to undergraduate students
Integration of physical bound constraints to alleviate shortcomings of statistical models for extreme temperatures
No full textInternational audienceHeatwaves have devastating impacts on societies and ecosystems. Their frequencies and intensities are increasing globally with anthropogenic climate change. Statistical models using Extreme Value Theory (EVT) have been used for quantifying risks of extreme temperatures but recent very intense events have cast doubt on their ability to represent the tail probabilities of temperatures. Using outputs from a large ensemble of a climate model, we show that physics-based estimates of the upper-bound of temperatures in the mid-latitudes are 3–8°C higher than suggested by EVT-based models. We propose a new method to bridge the gap between the physical and statistical estimates by forcing the EVT-based models to have an upper bound coherent with the bound provided by the instability of the air column. We show that our method reduces the underestimation of tail risks while not deteriorating the performance of the statistical models on the core of the distribution of extreme temperatures